from Service.start import render_template, request
#...
@app.route('/login/', methods=['post', 'get'])
def login():
    message = ''
    if request.method == 'POST':
	username = request.form.get('username')  # запрос к данным формы
	password = request.form.get('password')

    if username == 'root' and password == 'pass':
	message = "Correct username and password"
    else:
	message = "Wrong username or password"

    return render_template('login.html', message=message)